Lobothallia semisterilis

The thallus of Lobothallia semisterilis is placodioid in form and forms rather small, ground-hugging rosettes that usually do not exceed about 5 cm in diameter. It grows directly on soil and is held to the substrate by hyphae from the medulla rather than a well-developed lower cortex. Towards the centre, the thallus breaks up into small, angular areoles that are mostly flat to gently convex and around 1 mm across. The outer zone bears narrow, somewhat uneven lobes about 1 mm wide and 2–3 mm long, which radiate from the centre and give the thallus a lobate outline. The upper surface is pale, ranging from white to grey, and is covered by a dense pruinose layer; this pruinose coating becomes especially coarse and granular towards the lobe tips. The underside is white and lacks a distinct lower cortex. In vertical section the upper cortex is colourless with a slightly browned outer rim and is topped by a thin, colourless epinecral layer. Beneath this, the algal layer is relatively deep but occurs in discrete bands separated by narrow, almost algal-free gaps, and the medulla contains numerous grey granules.^[5]

Apothecia (sexual fruiting bodies) are common, appearing as low, rounded structures that narrow slightly at the base and reach about 2 mm across. Their disc is blackish-brown, flat to faintly convex and lacks pruina, and is encircled by a thalline margin that is the same colour as the surrounding thallus. The hymenium is hyaline and about 60 μm tall, topped by a brown, granular epihymenium; the paraphyses are simple with somewhat thickened tips, and the asci are eight-spored and belong to the Aspicilia type. Ascospores are ellipsoid, colourless and typically measure 9–13 × 5–9 μm. Pycnidia are abundant and conspicuous, often mimicking very small apothecia; they are 0.1–0.4 mm wide, with dark brown to blackish ostioles, and produce slender, bacilliform conidia about 5.5–6.5 × 1 μm. In standard spot tests the upper cortex reacts K+ (red) and is C− and P−, while the medulla is K+ (red), C− and P+ (yellow), a pattern that corresponds to the presence of norstictic acid as the main secondary metabolite.^[5]

Lobothallia semisterilis grows on soil in very dry, open habitats, including arid steppe and desert-like terrain, at mid to high elevations of about 1,760–3,150 m.^[5] It grows as part of biological soil crust communities on exposed soil, often intermingled with other terricolous lichens.^[6] It is known to occur only in north-western China, where it was originally collected in Gansu Province and has since been rediscovered there and in neighbouring Qinghai Province.^[5] It is one of 22 Lobothallia species recorded from China, where the genus reaches its greatest diversity in the arid mountains of the north and north-west.^[6]